Method for prestressing an axially retained homokinetic joint

ABSTRACT

The method permits mass-producing axially retained tripod joints having high rigidity and a given prestressing force which is reproducible from one joint to another. According to this method, after having clipped a resiliently yieldable attachment onto a tulip-shaped element of the joint while the joint is in its assembled position, the value of the gap between the shoulder of a thrust member and a bearing surface of a hub carrying the trunnions is determined for the position of the joint in which the hub and tulip-shaped member are in alignment and the thrust member is axially shifted away from the hub and there is introduced in the gap produced between the thrust member and the hub a shim the thickness of which is chosen to be slightly larger than the gap.

BACKGROUND OF THE INVENTION

The present invention relates to homokinetic joints and in particularsuch joints which allow a wide angular deviation between the two jointparts and comprise an axial retaining device.

The homokinetic joints of the invention are adapted to interconnect twoshafts or like members and comprise a first element in the shape of atulip rigid with one of the two shafts to be connected and definingraceways and a second element rigid with the other shaft and comprisinga hub from which extend the trunnions on which are rotatably andslidably mounted rollers received in the raceways of the first element.In a tripod joint the tulip-shaped element defines three raceways havinga part-circular section and each receiving a roller carried by each ofthe three trunnions of the second element which consequently has theshape of a tripod.

Such joints allow a wide angular deviation between the joint parts andare often axially fixed by providing between the tulip-shaped elementand the hub of the element carrying the trunnions an axial retainingdevice allowing, on one hand, a ball joint movement and, on the otherhand, a sliding movement in a direction perpendicular to the axis of oneof the two shafts. For this purpose, the tulip element is usually atleast partly closed by a resiliently yieldable attachment comprising aplurality of branches which are hooked onto corresponding branches ofthe tulip element, this attachment defining in its centre part aretaining surface for the hub of the element defining the trunnions.There is also provided at least one thrust member which is slidablymounted in the hub of the tripod element along the axis of theassociated shaft. This member usually has the shape of a mushroom whichhas a stem received in the hub and comprises a radial shoulder capableof coming in contact with a radial bearing surface of the hub.

It has been found that in certain applications, and in particular infront-drive vehicles, such joints are subjected to vibrations producedby the vehicle driving engine unit, the state of the road and variousfrictions. The axial retaining system is then stressed cyclically and toobtain a silent and durable operation, two conditions must be satisfied,namely:

1. A given prestressing force must be exerted in the axial retainingdevice.

2. The axial rigidity of this retaining device must be as high aspossible in order to avoid that it be put into resonance under theeffect of the cyclic excitations coming mainly from the engine.

Now, these two conditions are practically impossible to satisfysimultaneously since the prestressing force to be exerted depends to alarge extent on the algebraic sum of the manufacturing tolerances of thevarious component parts of the joint and in particular the tulipelement, the resiliently yieldable attachment, the hub of the tripodelement and the mushroom-shaped thrust member. Moreover, the clipping ofthe resiliently yieldable attachment can only be achieved under axialprestress since this clipping occurs when the joint is already in theassembled position and therefore under unfavourable conditions of accessand visibility.

SUMMARY OF THE INVENTION

An object of the invention is to provide a method and a device forprestressing a homokinetic joint which permits imparting to theprestressing device satisfactory rigidity and prestressing force whileallowing an easy, rapid and reliable assembly of the joint applicable tomass-production.

The method according to the invention is mainly applicable to a jointsuch as that defined hereinbefore in which the axial retaining devicecomprises at least one thrust member slidably mounted in an axial borein the hub, this thrust member comprising a radial shoulder in facingrelation to a radial bearing surface of the hub, and a resilientlyyieldable attachment fixed to the end of the tulip element. According tothis method, after having clipped the resiliently yieldable attachmentonto the tulip element while the joint is in the assembled position, thevalue of the gap between the shoulder of the thrust member and thebearing surface of the hub is determined for the position of alignmentof the two joint parts, the thrust member is moved axially away from thehub and there is introduced between the thrust member and the hub a shimwhose thickness is so chosen as to be slightly greater than said gap.Preferably, the thrust member is shifted axially away from the hub bybringing the joint to its position corresponding to maximum angulardeviation of the joint parts.

Another object of the invention is to provide a homokinetic jointcomprising a tulip element defining raceways for rollers rotatably andslidably mounted on trunnions rigid with a hub, axial retaining meansbetween the tulip element and the hub and comprising at least one thrustmember which is axially slidably mounted in the hub and has a radialshoulder in facing relation to a radial bearing surface of the hub and aresiliently yieldable attachment fixed to the end of the tulip element,wherein there is provided between the radial shoulder of the thrustmember and the adjacent radial bearing surface of the hub a shim formedby a resiliently yieldable ring clipped on the thrust member and havingan axial thickness which is slightly greater than the gap between theradial shoulder and the adjacent radial surface of the hub when thejoint is in the position of the alignment.

By means of this method, it is sufficient to have available a certainnumber of shims of different thicknesses to choose for each joint theshim which provides the desired prestressing force independently of thenormal manufacturing tolerances of the different component parts of thejoint and its axial retaining device.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments of the invention will be described hereinafter withreference to the accompanying drawings which are given by way of exampleand in which:

FIGS. 1 to 3 are longitudinal sectional views of a joint according tothe invention at three different stages of the prestressing method;

FIG. 4 is a detail view on an enlarged scale of a first embodiment of ashim which is part of this joint;

FIG. 5 is a view of a modification of this shim;

FIG. 6 is a longitudinal sectional view of the joint in the assembledposition, and

FIG. 7 is a view similar to FIG. 6 of a modification of the joint.

DETAILED DESCRIPTION OF THE INVENTION p FIG. 1 shows two shafts 1, 2 tobe interconnected by a homokinetic joint according to the invention. Theshaft 1 is rigid with an element 3 in the shape of a tulip andcomprising three branches 4 which define three raceways 5 ofpart-circular section. The shaft 2 is rigid with a bowl-shaped element 6in which is fixed an element 7 in the shape of a tripod comprising a hub8 and three trunnions 9 on which are rotatively and slidably mountedpart-spherical rollers 10 received in the raceways of the tulip element.In the illustrated embodiment, the hub defines an axial bore 11 in whichthere is received a mushroom-shaped thrust member 12 comprising acylindrical stem 13 and a thrust surface 14 defining a part-sphericaldome. This thrust member also has a radial shoulder 15 which is infacing relation to a radial bearing surface 16 of the hub. A compressionspring 17 is interposed between the inner end of the bore or cavity 11and the member 12. The axial retaining device is completed by aresiliently yieldable attachment 18 which defines a surface 19 adaptedto bear against a part-spherical surface 20 of the hub and threebranches 21 which are resiliently clipped onto the branches of thetulip-shaped element in the known manner which consequently need not bedescribed in detail.

The prestressing method according to the invention is carried out in thefollowing manner: the attachment 18 is previously introduced in thebowl-shaped element 6. The tulip-shaped element is fitted on the threerollers 10 and inclined at an angle in the neighbourhood of the maximumangle of deviation as shown in FIG. 1 so as to depress the thrust member12 and cause it to bear by its shoulder 15 against the bearing surface16 of the hub. The tulip element is then in its inner position in thebowl-shaped element 6 and the clipping of the branch 18 of theresiliently-yieldable attachment through which passes the plane of theaxes X--X and Y--Y of the two shafts 1 and 2 can be easily achieved onthe corresponding branch of the tulip element. The clipping of the othertwo branches of this attachment is achieved in the same way by pivotingthe tulip element in the planes of these other two branches. Note thatat this stage, apart from the fact that the relatively low axial forceexerted by the spring 17 should be overcome, this operation is carriedout in the absence of any axial prestress.

When the tulip element is released, and the two shafts are brought totheir position of alignment (FIG. 2), a gap appears between the shoulder15 and the surface 16 of the hub. This gap may be measured at thismoment, for example by an axial displacement of the tulip element to aposition in which the shoulder 15 abuts against the surface 16 or bymeans of a special gauge. By way of example, this gap may vary betweenabout 0.5 and 1.5 mm.

The joint is then brought to its position of maximum angular deviationbetween the joint parts (FIG. 3) by a rotation about one of thetrunnions of the tripod element, which permits a maximum access to thethrust member 12 and increases the gap between the shoulder 15 and thebearing surface 16 and permits sufficient access to the thrust member 12to allow the introduction of a shim 22 (FIG. 3) which is in the form ofa resiliently yieldable split ring. The axial thickness of this shim isso chosen as to slightly exceed the value of the aforementioned gapmeasured in the position shown in FIG. 2 so that, when the joint is putback into the position corresponding to an alignment of the joint partsafter introduction of the shim, the desired prestress is automaticallyobtained.

The excess thickness of the shim relative to the measured dimension orgap is constant for a given type of joint. It is determinedexperimentally in accordance with the axial rigidity of the resilientlyyieldable attachment 18 and the value of the desired prestressing force.It is desirable to have available a series of shims of differentthicknesses, the thickness difference between two successive shims maybe from 1/100th of a millimeter to 1/10th of a millimeter, so that allthe gaps resulting from the manufacturing tolerances of the variouscomponent parts of the assembly may be compensated for and the value ofthe desired prestressing force obtained with precision.

In the embodiment shown in FIG. 4, the resiliently yieldable split ring22^(a) constituting the shim has a wrap-around angle e₁ which issufficient to ensure that it is maintained on the stem 13 of the thrustmember 12. In this embodiment of FIG. 4, it has a roughly constantradial width and an end chamfer 23 which facilitates its mounting.

In the embodiment shown in FIG. 5, the split ring 22^(b) has a morecomplex shape and in particular a variable radial width which permits animproved distribution on the faces of the pressure resulting from theprestressing force and increasing the wrap-around angle e₂ withoutincreasing the force required for mounting the ring on the stem. Forthis purpose, the ring has two roughly diametrally opposed zones 24 ofminimum width and two end zones 25 of increased radial width terminatingin bevels 26. The bore 27 is moreover slightly eccentric relative to theperiphery 28. The pressure is thus evenly distributed on the two sides.

In the embodiment just described, which is shown assembled in FIG. 6,the axial retaining device comprises a spring 17 between the thrustmember 12 and the inner end of the cavity 11 in the bore.

The function of this spring is to facilitate the assembly for taking upthe clearances appearing in certain configurations. However, such aspring is not essential and there is shown in FIG. 7 an embodiment inwhich this spring is eliminated. However, in order to be able to measurethe gap between the shoulder 15 of thrust member 12 and the adjacentbearing surface 16 of the hub, there should be exerted on the tulipelement when the joint is in its position shown in FIG. 2 a pull and adepression. The displacement of the tulip element between these twopositions is measured with precision and permits a determination of theclass of the shim likely to provide the desired prestressing.

It is clear from the foregoing that the method and device according tothe invention achieve the desired objectives. Thus, the method may beemployed on an industrial scale and in mass-production and the rigidityof the resiliently yieldable attachment may be considerable whileproviding a precise prestressing force which is reproducible from onejoint to another. This results from the fact that the shim, whichdetermines the value of this prestressing force, is placed in positionafter measuring for each joint the real gap between the shoulder of thethrust member and the adjacent bearing surface of the hub.

Having now disclosed in my invention what I claim as new and desire tosecure by Letters Patent is:
 1. A method for axially prestressing ahomokinetic joint comprising a first tulip element for rigidlyconnecting to one of two shafts to be interconnected and definingraceways, a second element for rigidly connecting to the other of saidshafts and comprising a hub and trunnions extending from the hub, thehub defining an axial bore and a radial bearing surface, rollersrespectively rotatively and slidably mounted on the trunnions andreceived in the raceways of the first element, an axial retaining devicecomprising at least one thrust member slidably mounted in the axial boreof the hub, said thrust member comprising a radial shoulder in facingrelation to the radial bearing surface of the hub, and a resilientlyyieldable attachment fixed to an end of the tulip element, said methodcomprising, clipping the resiliently yieldable attachment onto the tulipelement while the joint is in an assembled position, then determiningfor a position of alignment of said first and second elements the sizeof a gap between the shoulder of the thrust member and the bearingsurface of the hub, axially shifting the thrust member away from thehub, and introducing between the thrust member and the hub a shim havinga thickness which is so chosen as to be slightly larger than said gap,thereby providing an axial prestress between said thrust member and saidhub and thus between said first and second elements.
 2. A method asclaimed in claim 1, comprising measuring said gap by axially displacingthe tulip member when the joint is in the position of alignment of saidfirst and second elements until the shoulder is brought into abuttingrelation to the bearing surface of the hub.
 3. A method as claimed inclaim 1, comprising measuring said gap by exerting a pull on the tulipelement when the joint is in the position of alignment of said first andsecond elements, and then depressing the tulip-shaped element until theshoulder is brought into abutting relation to the bearing surface of thehub.
 4. A method as claimed in claim 1, comprising axially shifting thethrust member away from the hub by bringing the joint to its position ofmaximum angular deviation between said first and second elements.